Research On Key Technologies For Fm Capacitive Displacement Sensor

As capacitive displacement sensor has the advantages of high resolution, high frequency response and non-contact measurement, it can measure the rotational accuracy of rotating shaft, reciprocating movement and the dimensions, straightness measurement of workpiece, so it is widely used in the field of ultra-precision positioning and ultra-precision measurement. Currently, ultra-precision machining technology is developing rapidly in the field of microelectronics manufacturing, micro-optical devices and micro-machining, the micro-displacement sensor which has high frequency response, high resolution and high signal to noise ratio has become an important research direction.Researching on the key technologies in the FM capacitive displacement, the paper solves kinds of critical technical problems in FM capacitive sensor such as stability, zero drift and nonlinear error and in this basis improve the sensitivity of displacement sensors and anti-jamming capability. Via studying the making method of sensor deep and integrating digital circuits and analog circuits, the paper develops the FM capacitive displacement sensor using difference frequency FM technology. The main research is as follows:1. Using the advantage of FM circuit with good anti-electromagnetic interference capability and transmission, LC oscillator not only achieve high oscillation frequency (3.7MHz) but also increase the modulation sensitivity by the dual differential frequency, and provide the conditions for improving the detection sensitivity of IF.2. Aiming at the problem in FM capacitive sensor that LC oscillator's frequency drifts with temperature randomly resulting in poor stability of sensor and poor output signals, the paper improves AC input impedance of the oscillator circuit to suppress the drop of oscillation circuit Q via designing the rational circuit to decrease the distributed capacitance between the poles and the load resistance on the frequency stability. At the same time, the paper uses hardware temperature compensation technology to inhibit temperature drift for frequency stability.3. Research on frequency detector based on transformer coupling deep, the frequency discrimination method not only has broad frequency response but also improve the linearity of the sensor by adjusting the frequency detector characteristic curve to compensate for the nonlinear error of the capacitive sensor. 4. I design the fourth-order Butterworth filter to suppress the impact of sensing measurement signal by noise aiming at the high-frequency electronic noise in capacitive sensor. At the same time, I correct the inherent nonlinear error in sensor by look-up table method.Finally, the performance of the sensor is tested. Experimental results show that the resolution of LC oscillator circuit is up to 5nm, the non-linearity less than 3% and the oscillator frequency stability is 1.55×10^-6.